Prop size for heavy Chapparall

[johnny be good]

Hello, Thanks for taking the time to read this question even though I don't have all the info that I know is important to make a recomendation but I am only at this time trying to get in the ball park. First off I have an older very heavy Chapparall Teak wood interior which adds a lot of weight this boat is our cabin on the water it is full of food supplies human and dog, pots and pans, clothing for a week grill, coolers well you get the picture. I average 1500-2000 rpm putting from point A to B about 3miles to our camp spot. I never try to get on plane but would like to get somewhere in the ballpark with the right prop. I had a new engine coupler installed this year and I changed my prop but the performace has dropped. I was given a stainless prop to tryout it is a Merc Vengeance 48-16318A45 13 3/4 x 21p the boat will not throttle up at all without a lot of noise so I can not give a wot spec. I think the prop that was on it bfore was around 15 1/4 x 15p it averaged about 3500-4000 wot as I stated before I don't really jump on it at all. Am I way off on the Vengeance prop ? Where about should I be trying fo prop size. 350 Merc Cruise engine not Magnum Alpha 1 outdrive new gimble bearing and u joints. Thanks for reading and will get wot rec. off engine this week.

 

[steelespike]

Re: Prop size for heavy Chapparall

"Very heavy Chapparall" is a little vague but Based on your numbers with the 15" prop.
We have a ball park size.We really need the rpm and gps speed to evaluate the setup.
The 21 appears to be too much prop.
For motor health and performance the it needs to be able to rev freely close to the max rated rpm, probably 4600-4800,
regardless of how you drive it.
It does appear that the 15 is too much prop.The 21 seems to be way too much makes it harder for the motor to push the boat.
A number of things can slow the boat.Is the bottom clean and smooth? Is the motor in excellent tune,timing set right and advancing as it should.Is the throttle opening all the way?

 

[johnny be good]

Re: Prop size for heavy Chapparall

Thanks steelespike I will be putting the other prop on this weekend at least with that one I can open up the throttle to see where I am with rpms . I tried the 21p prop because my other one was alum. and had a nick in one blade the repair shop didn't want to repair it because it had been repaired to many times before I got it with the boat. The 21 p Vengaence was to radical to even try to try to open it up. With the alum prop on should I run it with the outdrive down or try to get it up on plane before checking rpms ? I will also check sticker on the engine to see where it should run. The numbers on the alum. prop are gone but was told it was a 15 1/4 x 15 it seem to run ok but I don't want to buy a new one just to try it out I am trying to get close to what I need before hand. To bad theres not a way to try a prop before so you will know, I am wanting to go stainless and there not cheap. The engine is in tune and runs great the boat was cleaned just before putting in. Thanks again John

 

[steelespike]

Re: Prop size for heavy Chapparall

For the test you alone or one other person. wot rpm and speed trimmed for the fastest.
There may be numbers under the prop nut.
There are dealers that will let you test props with the understanding you're going to buy.
Usually requires a sizable deposit.

 

[johnny be good]

Re: Prop size for heavy Chapparall

Sorry I keep saying that I will be testing this weekend but I'm meaning this upcomming weekend will keep you posted

 

[steelespike]

Re: Prop size for heavy Chapparall

No problem get the info to us when you can.